Copying system featuring alternate developing and cleaning of successive image areas on photoconductor

ABSTRACT

Electrophotographic copying apparatus has charging, imaging, transferring, precleaning, and erasing facilities in a conventional sense but incorporates a combined developingcleaning unit that is operable to perform either function at the proper time during the copying sequence. A first version incorporates a photoconductor drum structure surrounded with the necessary electrophotographic elements including a single magnetic brush developer-cleaner unit, the drum structure preferably having an odd number of image areas, such as three. Another version incorporates a photoconductor belt also having provision for an odd number of image areas and movable past the stations. For single copy operation, alternate image positions are used for copying with cleaning occurring on the positions between. With the operator changing masters, this delay is not noticeable. With an automatic document feeder, the throughput rate is half of the continuous copy rate. For continuous copy, every image position is used and cleaning is suspended until the end of the run at which time a full cycle cleaning operation is initiated. If the run is long and the copy degrades, intermediate cleanup cycles can be included as often as necessary. Conveniently, a magnetic brush element forms a contacting surface for conveying toner onto the photoconductor surface during developing and away from the photoconductor surface during cleaning. Appropriate changes in biasing of the brush are made during operation.

United States Patent Cooper [is] 3,637,306 [451 Jan. 25, 1972 [54] COPYING SYSTEM FEATURING ALTERNATE DEVELOPING AND CLEANING OF SUCCESSIVE IMAGE AREAS ON PHOTOCONDUCTOR [72] Inventor:

[73] Assignee:

Leon M. Cooper, Lexington, Ky.

[22] Filed: Dec. 2, 1970 211 Appl.No.: 94,262

[57] ABSTRACT Electrophotographic copying apparatus has charging, imaging, transferring, precleaning, and erasing facilities in a conventional sense but incorporates a combined developingcleaning unit that is operable to perform either function at the proper time during the copying sequence. A first version incorporates a photoconductor drum structure surrounded with the necessary electrophotographic elements including a single magnetic brush developer-cleaner unit, the drum structure preferably having an odd number of image areas, such as three. Another version incorporates a photoconductor belt also having provision for an odd number of image areas and movable past the stations. For single copy operation, alternate image positions are used for copying with cleaning occurring on the positions between. With the operator changing masters, this delay is not noticeable. With an automatic document feeder, the throughput rate is half of the continuous copy rate. For continuous copy, every image position is used and cleaning is suspended until the end of the run at which time a full cycle cleaning operation is initiated. If the run is long and the copy degrades, intermediate cleanup cycles can be included as often as necessary. Conveniently, a magnetic brush element forms a contacting surface for conveying toner onto the photoconductor surface during developing and away from the photoconductor surface during cleaning. Appropriate changes in biasing of the brush are made during operation.

,6 q qiw 39m ns "89 IIII/IIIIIIIIIII/IIIIIII/IIIIIIIIIIIIIlIIIIIII/l [52] US. Cl ..355/15,117/17.5, 118/637 [5 I] Int. Cl. ..G03g 15/00 [58] Field otSearch ..95/15; 117/17.5; 118/637;

134/1 I [56] References Cited UNITED STATES PATENTS 2,874,063 2/1959 Greig ..1l7/17.5 2,911,330 11/1959 Clarkm. 134/1 2,986,442 5/1961 Broding .346/74 3,572,923 3/1971 Fisher et a1. .....355/15 3,580,673 5/1971 Yang ..355/15 Primary ExaminerSamuel S. Matthews Assistant Examiner-Richard M. Sheer Atlorney-Hanitin and Jancin and D. Kendall Cooper RAFFmFnJAuzs so El PRECLEAN ERASE FIG. 3

INVENTOR LEON M. COOPER ATTORNEY 1. COPYING SYSTEM FEATURING ALTERNATE DEVELOPING AND CLEANING OF SUCCESSIVE IMAGE AREAS ON PI-IOTOCONDUCTOR RELATED PATENT APPLICATION U.S. Pat. application Ser. No. 94,037 filed Dec. 1, 1970 with Carl A. Queener as inventor, and entitled Copying SystemFeaturing Combined Developing-Cleaning Station Alternately Activated.

BACKGROUND OF THE INVENTION AND PRIOR ART tive belt has an associated magnetic brush 24 operable at one station to develop images on the belt and at an independent second station to clean residual developer material from the belt. Broading shows no means for alternately activating a common magnetic brush that is in contact at a single station with a photoconductor medium and for applying an appropriate bias to the magnetic brush depending upon whether a developing mode or a cleaning mode is required.

SUMMARY OF THE INVENTION In accordance with the present invention, electrophotographic apparatus having a photoconductor medium, such as a segmentized drum, is provided with the usual facilities for charging, imaging, developing, cleaning, transferring, precleaning, and erasing during the process of producing copies from an original document with the significant exception that a combined unit is provided in the apparatus for perfonning both the developing and cleaning functions in proper timed sequence with respect to the successive cycles of rotation of the medium and of the individual segments or frames thereon. In the preferred embodiments described herein, such combined unit incorporates a magnetic brush element with biasing means to establish appropriate biasing to initiate transfer of toner onto the photoconductor surface in the apparatus during the developing step and to attract residue residual toner from the photoconductor surface during the cleaning operation. As will be described in greater detail, circuitry is also provided for effecting a cyclical sequence that establishes the most effective use of the structures during multiple cycle operation.

In a first version, FIG. I, a magnetic drum photoconductor structure preferably has an odd number of segments, such as three segments or frames designated frame A, frame B, and frame C with timing of the various steps of the copying process being keyed into the rotation of the drum and the movement of the respective frames past the various stations during operation. In a typical sequence termed mode 1 operation, the first cycle of the drum includes imaging and developing of frame A and frame C and cleaning of frame B, During the second typical cycle, the sequence involves cleaning of frames A and C and imaging of frame B. The sequencing described is continued in this manner during succeeding cycles of rotation of the drum.

As an alternative, it is possible to image each frame on the photoconductor drum during each and every rotation of the drum without skipping any frames for the cleaning operation and to withhold cleaning until a runout cycle or under other circumstances, such as when the'operator is changing the original document.

As set forth in the abstract, another version of the invention contemplates a photoconductor belt structure'with the belt having, as an example, seven image areas along its longitudinal dimension. Imaging can be by a scanning technique or flashing of lamps to expose an entire image area at once. Operation with a belt photoconductor may be comparable to that noted for the drum structure with alternate imaging and cleaning of the frame or image areas on the belt. Further, each frame can be imaged during each and every complete cycle of movement of the belt with the cleaning taking place during a cycle such as the runout cycle or during another interval that is convenient. As will be described in detail, various combinations of biasing of the magnetic brush, toner particles, and developer mixture may be incorporated in the apparatus for the intended purpose.

OBJECT'S Therefore, the primary object of the present invention is to provide electrophotographic apparatus for producing copies from original documents wherein a number of functions required during the process are performed in timed sequence by a combined unitary portion of the apparatus operable as required during operation. 5

Still another object of the present invention is to provide an electrophotographic apparatus requiring the charging, imaging, developing, cleaning, transferring, precleaning, and erasing of images on a photoconductor surface and wherein at least the developing and cleaning functions are performed by a common portion of the apparatus,

Another object of the invention is to provide a magnetic brush developer-cleaner unit for an electrophotographic apparatus that performs both functions in the system when and as required. 1

Also, an object of the invention is to provide a developingcleaning facility in an electrophotographic apparatus incorporating a magnetic brush element and having provision for appropriately biasing the brush to perform either a developing or a cleaning function during operation of the apparatus.

A further object of the invention is to provide a system of this nature with facilities for establishing timed sequences of electrophotographic steps enabling the alternate imaging and cleaning of image areas on a photoconductor surface to enable a sequence of developing followed immediately by cleaning.

In addition, an object of the present invention is to provide a system of this nature with provision for the production of a multitude of copies during an uninterrupted imaging sequence followed by a cleaning operation of all image areas on the photoconductor surface during the time not ordinarily used for copying purposes, such as runout time or other available time.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention as illustrated in the accompanying drawings.

DRAWINGS DETAILED DESCRIPTION First Embodiment with Photocondu ctor Drum, FIG. I

Turning now to FIG. 1, a typical electrophotographic copying device is schematically shown in conjunction with an embodiment of the invention. A cylindrical drum 21 having three segments or frames designated A, B, and C is mounted for rotation on a shaft. Drum 21 has on its outer periphery 23 a photoconductive insulating layer which contains an organic or inorganic photoconductive material. The drum 21 is rotated to bring the photoconductive layer to the various stations associated with the electrophotographic process. A variety of photoconductive materials are suitable for use, for example, selenium, selenium-tellurium, anthracene, zinc oxide in a resin binder, etc.

A preexposure corona unit 35 deposits a charge on the photoconductive material while it is maintained in the dark. A document 27 is held in place on a transparent plate 29, and an image of the document is projected on the surface of the photoconductive insulating layer by means of an illuminated scanning station 31 and optics 33. The photoconductor is discharged at 37 in the portions struck by light to form the charged image corresponding to the document 27, and the image is developed at combined developer-cleaning station 38 which serves to bring finely divided charged toner particles into contact with the charged image on the surface of the photoconductive layer. As set forth in the Queener application, the developer station is preferably a magnetic brush developer unit that serves both as developer and cleaner in the system. At station 38, a two component developer composition is caused to move across the surface of the photoconductive layer. The developer composition comprises relatively large carrier particles and relatively small heat fixable marking particles of toner. The toner particles are attracted to and cling to the charged areas of the photoconductor layer.

The rotating photoconductive surface is contacted by a driven counterrotating cylindrical magnetic brush 49, whose length corresponds approximately to the width of the photoconductive layer on the drum, of the structure illustrated in FIGS. land 2.

At station 39 the toner image on the surface of photoconductive layer 21 is transferred to a plain paper sheet or web 41 with the assistance of a toner transfer corona unit 43. The paper is then separated from the photoconductive layer and passed to a heating unit 45 which acts to fix the toner image onto the paper. The residual toner particles are loosened by the discharge of a preclean corona unit 47.

In accordance with the first embodiment of the invention, the sequencing of the various stations in the system is set up as follows:

timed relation with movement of belt 12.

returning to its home position during a portion of each frame revolution as the related frame to be cleaned is passing through the imaging and developer/cleaner station.

Second Embodiment with Photoconductor Belt, FIG. 2

FIG. 2 illustrates another embodiment of the invention where the electrophotographic apparatus incorporates a photoconductor belt movable in 'timed relation in the system to perform all of the various process steps in a manner comparable to that set forth previously in the table. As shown, the apparatus of FIG. 2 incorporates a combined developingcleaning unit 17 that serves a function comparable to that in the drum-oriented system of FIG. 1.

The unit in FIG. 2 includes various electrophotographic facilities for producing copies. These include a charge corona station 18, the image plane 12a, previously mentioned, a developer-cleaning station 17, a transfer station 19, and a preclean corona station 20. Belt 12 is mounted for movement as indicated by arrow 15 on drum driving elements 14 and 16. A paper supply 11 accommodates a large quantity of individual sheets of paper that are fed by various devices including a belt 10 to the transfer station 19 for transfer of images in Following such transfer, the image is fused by a fuser, not shown, and transported to a completion station.

Sequencing of the developing-cleaning station 17 in the belt version of FIG. 2 may be comparable to the sequencing for the drum version of FIG. 1.

FIG. 3 is a suggested circuit for accomplishing the sequencing set forth in table A above. Depression of start button gates drum cycle circuit 62 that provides cycle 1, cycle 2, and cycle 3 outputs as shown. Rotation of drum 21 is recognized to provide timed impulses to drum cycle circuit 62 and frame circuit 63 that provides frame A, frame B, and frame C control signals as shown. Various AND and OR circuits at 65 are activated to gate the charge, image, develop, clean, transfer, and preclean and erase control blocks that are operable in sequence and that provide outputs on lines 67. If the photoconductor is erased as shown in table A, then the bias level for both developing and cleaning is normally the same. If the photoconductor is not erased and cleaning is desired then the bias must be altered by control circuit 50 to insure that it is more negative than the residual image remaining on the photoconductor.

Same as drum revolution 1 Same as drum revolution 2 As shown in the table, frames occurs in an alternate fashion throughout the various cycles of rotation of drum structure 21. Thus, frames A and C are imaged during drum cycle 1 while frame B is cleaned; frame B is imaged during drum cycle 2 while frames A and C are cleaned. In a typical case, the optical scanning system is imaging of frames and cleaning of With the embodiment of FIG. 1 and the sequencing shown, ,cleaning of image areas, that is, frames A, B, etc., on the surface of drum 21 occurs in the cycle of rotation of drum 2] immediately following the imaging and developing of the frame in question. I

As indicated, it is further contemplated that a multitude of copies, such as 200, can be imaged, developed. transferred. 3

Should it prove feasible to repeat copies without cleaning, then a sequence for six copies could be:

6 i l. Electrophntographic apparatus for producing at least one copy from an original document and having the customary electrophotographic facilities for charging. imaging. transfer ring. precleaning. and erasing a photoconductor medium. said photoconductor medium comprising a movable member havduring joperation of said apparatus. compnsmg:-

a combined developer-cleaner unit positioned for engagement with said photoconductor medium at a single station for developing an image in one mode and cleaning said photoconductor medium in another mode; and

TABLE B Develop Preclean or Frame Charge Image clean Transfer erase Drum revolution:

With respect to the cleaning after multiple runs of copy, it is possible to arrange the system in such a manner that a cleaning operation occurs more frequently, such as, in one out of every five copies, rather than after the entire run of a large number of copies is performed.

Other parameters to be considered are as follows.

The preclean/erase station may be optional. Without it, the

developer bias would have to be switched to a value below the cleaner without changing the bias.

in a normal copy sequence, the charge levels on the photoconductor would be as follows (The actual values shown are representative and not necessarily exact):

0 --Preclean/Erase --l--------------------------'Deve1oper Bias 400 U U U -600 Dark Image Level qlfyel V Background Level From this it can be seen that the toner, which is positive, will be attracted from the developer to the dark image areas (more negative) but not the background (less negative). Also, if the preclean-erase restores the level of the photoconductor and residual toner to a value significantly more positive than the developer bias, the positive toner will be attracted to the negatively biased developer. In this case, the bias of the developer need not be changed to make it function as a cleaner. if, however, the photoconductor and residual toner ends the cycle close to (or more negative than) the developer bias, then that bias must be changed to a more negative value by a control circuit 50 in order for the developer to operate effectively as a cleaner.

While the invention has been particularly shown and described with reference to several embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.

What is claimed is:

and

sequencing means for activating said developer-cleaner unit to alternately develop and clean successive image areas during rotation of said drum member.

2. The apparatus of claim 1; wherein said photoconductor medium is in the form of a rotatable cylindrical drum member. and further comprising: 1 7

means for rotating said drum member during successive cycles of operation of said apparatus to produce a multitude of copies; 4 means to activate said developer-cleaner unit in a developer mode continuously during said successive cycles of operation of said apparatus and rotation of said drum member; and

runout means operable upon termination of said successive cycles and production of a multitude of copies to activate said developer-cleaner unit to clean said photoconductor drum member copy run.

3. The apparatus of claim 1, wherein:

said photoconductor medium is in the form of an endless belt member mounted for movement in a preferred direction to convey image areas past the various stations in said apparatus during operation; and

means for activating said developer-cleaner unit to alternatively develop and clean successive image areas on said belt member.

course of producing copies, and further comprising:

means for activating said developer-cleaner unit to develop each succeeding image on said photoconductor belt member during operation and the production of a multitude of copies; and

means for activating said developer-cleaner unit to clean said photoconductor belt member upon termination of a run of said multitude of copies.

5. The apparatus of claim I wherein said developer-cleaner unit comprises a housing to accommodate a developer mixture including tonenand further comprising:

a magnetic brush mounted within said housing and in contact with saidphotoconductor medium at a single station for conveying developer mixture onto said photocond uctor medium in one mode for the purpose of developing images on said photoconductor medium and for applying developer mixture onto said photoconductor medium in a in readiness for a succeeding multiplescavenging mode for the photoconductor medium; and

sequencing means for activating said developer-cleaner unit and said magnetic brush member in the appropriate mode required during operation of said apparatus.

6. The apparatus of claim 5, further comprising:

means for producing positive and negative biasing potentials; I

means connecting said magnetic brush member to said potential producing means during operation of said apparatus; and

purpose of cleaning said 

1. Electrophotographic apparatus for producing at least one copy from an original document and having the customary electrophotographic facilities for charging, imaging, transferring, precleaning, and erasing a photoconductor medium, said photoconductor medium comprising a movable member having an endless surface with an odd numbered plurality segments on said surface to accommodate a plurality of successive image areas thereon during operation of said apparatus, comprising: a combined developer-cleaner unit positioned for engagement with said photoconductor medium at a single station for developing an image in one mode and cleaning said photoconductor medium in another mode; and sequencing means for activating said developer-cleaner unit to alternately develop and clean successive image areas during rotation of said drum member.
 2. The apparatus of claim 1, wherein said photoconductor medium is in the form of a rotatable cylindrical drum member, and further comprising: means for rotating said drum member during successive cycles of operation of said apparatus to produce a multitude of copies; means to activate said developer-cleaner unit in a developer mode continuously during said successive cycles of operation of said apparatus and rotation of said drum member; and runout means operable upon termination of said successive cycles and production of a multitude of copies to activate said developer-cleaner unit to clean said photoconductor drum member in readiness for a succeeding multiple-copy run.
 3. The apparatus of claim 1, wherein: said photoconductor medium is in the form of an endless belt member mounted for movement in a preferred direction to convey image areas past the various stations in said apparatus during operation; and means for activating said developer-cleaner unit to alternatively develop and clean successive image areas on said belt member.
 4. The apparatus of claim 1 wherein said photoconductor medium is an endless belt member mounted for movement in a preferred direction during operation of said apparatus to convey successive image areas past the various stations in the course of producing copies, and further comprising: means for activating said developer-cleaner unit to develop each succeeding image on said photoconductor belt member during operation and the production of a multitude of copies; and means for activating said developer-cleaner unit to clean said photoconductor belt member upon termination of a run of said multitude of copies.
 5. The apparatus of claim 1 wherein said developer-cleaner unit comprises a housing to accommodate a developer mixture including toner, and further comprising: a magnetic brush mounted within said housing and in contact with said photoconductor medium at a single station for conveying developer mixture onto said photoconductor medium in one mode for the purpose of developing images on said photoconductor medium and for applying developer mixture onto said photoconductor medium in a scavenging mode for the purpose of cleaning said photoconductor medium; and sequencing means for activating said developer-cleaner unit and said magnetic brush member in the appropriate mode required during operation of said apparatus.
 6. The apparatus of claim 5, further comprising: means for producing positive and negative biasing potentials; means connecting said magnetic brush member to said potential producing means during operation of said apparatus; and means operable as successive image areas on said photoconductor on drum are processed for selectively applying one or the other of said potentials as a bias to said magnetic brush member to create the repulsion necessary to transmit developer mixture from said magnetic brush member to said photoconductor medium during a developing mode and to create the attraction relationship to scavenge developer mixture from said photoconductor medium to said magnetic brush member during a cleaning mode. 